I have used the the software modem under G3RUH-BPSK folder. The audio is fed from an Icom 821H using a Signalink USB + doppler correction, tried in both FM and USB mode but no decode. Will try the signal centered on the 2000 Hz mark as suggested. 73 Nitin [VU3TYG]

From: Scott scott23192@gmail.com To: Ken Swaggart k.swaggart@charter.net Cc: AMSAT BB amsat-bb@amsat.org Sent: Wednesday, 17 January 2018 10:28 PM Subject: Re: [amsat-bb] PicSat demodulator?

Despite the documentation, PicSat beacons so far have been 1k2 BPSK.

There is a 1k2 BPSK software modem in:

http://uz7.ho.ua/modem_beta/other-versions.zip

... and the demod on that would be USB.  Of course the bandwidth & centering of the audio output is critical for this scheme; what works well for me is to output the audio (I use HDSDR into VB Audio virtual cable) at 4 KHz with the signal centered on the 2000 Hz mark.  If you match that 2000 Hz center on the 1k2 BPSK software modem screen, it decodes very nicely.

-Scott,  K4KDR

================================

On Wed, Jan 17, 2018 at 11:19 AM, Ken Swaggart k.swaggart@charter.net wrote:

Have been trying to decode the 435.525 MHz beacons from PicSat without success. The modulation is described as "GMSK modulation with G3RUH scrambling". I'm assuming the baud rate is 9600.  Normally I use UZ7HO's High-Speed SoundModem for telemetry reception.

Tnx, Ken, W7KKE

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El 17/01/18 a las 17:56, Scott escribió:

Despite the documentation, PicSat beacons so far have been 1k2 BPSK.

There is a 1k2 BPSK software modem in:

http://uz7.ho.ua/modem_beta/other-versions.zip

... and the demod on that would be USB. Of course the bandwidth & centering of the audio output is critical for this scheme; what works well for me is to output the audio (I use HDSDR into VB Audio virtual cable) at 4 KHz with the signal centered on the 2000 Hz mark. If you match that 2000 Hz center on the 1k2 BPSK software modem screen, it decodes very nicely.

Hi all,

As Scott said, the complete description for PicSat's mode is 1k2 BPSK AX.25 with G3RUH scrambler.

UZ7HO's soundmodem should works nicely with this, but for the adventurous, there is also a GNU Radio based decoder in gr-satellites. For this, the signal should be centered at the 1500 Hz mark (though you can change this setting).

The integrated telemetry decoder is underway (at least some form of it).

I've yet to optimize the gr-satellites decoder, but I've noted that PicSat's signal almost fills a typical 2700Hz bandwidth (it's nominally 2400Hz wide), so no wonder that tuning is critical. Perhaps I'll do another decoder that works on "wide SSB" (up to 24kHz width, with the signal on the 12kHz mark), as is typically used for the wider 9k6 BPSK modes. Using the "FLL Band edge" in GNU Radio, it should be possible to correct automatically around 500Hz of mistuning.

Also, there is a decoder from the PicSat team that runs on Windows and Linux. I haven't downloaded it, and I'm not even sure if it has been released in public (other than in its Github repo), but I've heard that it even searches for the signal (like the FUNcube dashboard or FOXtelem) so you don't even have to worry about tuning.

73,

Dani.